1. Field of the Invention
The present general inventive concept relates in general to an image processing device capable of selecting a field and a method thereof. More specifically, the present general inventive concept relates to an image processing device which is capable of selecting a field to use in interpolation if an input image is a film image, and a method thereof.
2. Description of the Related Art
Cinema films are typically recorded at 24 frames per second. Each frame is instantly stored on film and shot on a screen at one time, producing a progressive image together. On the other hand, TVs have different image processing speeds (or frame rates) that depend on TV transmission systems. For example, NTSC (National Television System Committee) runs at 30 frames per second, whereas PAL (Phase Alternation Line) and SECAM (Sequential Couleur Memoire) videos run at 25 frames per second. Since TV broadcasts transmit an image using radio waves, the number of scanning lines of each frame ranges several hundreds for photographing and transmission thereof, and the image is displayed on a cathode ray tube through scanning.
In order to show motion pictures more effectively with a limited number of scanning lines, TV usually adopts an interlacing method where a frame is divided into two fields, which are alternately scanned. Therefore, the NTSC system processes an image at 60 fields per second, whereas the PAL and the SECAM systems process an image at 50 fields per second.
On the other hand, when a cinema film is played back on a TV monitor at a TV frame rate, an image on an NTSC television system (which runs at 30 frames per second) will look faster because the number of frames per second differs in a movie screen and the TV monitor. Therefore, in a case in which a cinema film is transmitted to the NTSC television system, 60 fields must be obtained from 24 frames per second, namely, 5 fields from 2 frames, to synchronize the cinema film with the NTSC television system. In general, a 3:2 pull-down technique is most commonly used for converting 24 frame per second motion picture material to 60 field per second video and NTSC. In the 3:2 pull-down, one film frame is scanned into three fields and the next frame is scanned into two fields. That is, 2 frames are scanned into five fields. On the other hand, when a cinema film is played back on a PAL television system or a SECAM television system, 50 fields must be created from 25 frames per second, i.e., 2 fields from each frame. This method is called a 2:2 pull-down, where each film frame is scanned into two frames. Normally, one frame of a film is composed of a top field with odd lines and a bottom field with even lines. Thus, in order to create 3 fields for film to video conversion in the 3:2 pulldown, one of the top and bottom fields is repeated.
FIG. 1 is a block diagram illustrating a conventional image processing device.
Referring to FIG. 1, the conventional image processing device includes a pattern generation unit 10, a film determination unit 20, and an interpolation unit 30. The pattern generation unit 10 calculates a difference in pixel values between fields for three temporarily consecutive fields of an input image, and generates a pattern with respect to a predetermined threshold. For example, the pattern generation unit 10 calculates a difference in pixel values between two temporarily consecutive fields, such as a first field and a second field. If the difference in the pixel values is greater than the predetermined threshold, the pattern generation unit 10 generates a “1”, whereas if the difference in pixel values is less than the predetermined threshold the pattern generation unit 10 generates a “0”, thereby generating the pattern.
The film determination unit 20 determines whether an input image is a film image, based on the pattern generated by the pattern detection unit 10. Since a film image usually has a certain pattern, it is possible to determine whether the input image is a film image or not by comparing the pattern generated by the pattern detection unit 10 with a pre-stored film image pattern.
The interpolation unit 30 interpolates the input image according to the determination made by the film determination unit 20. That is, if the film determination unit 20 determines that the input image is not a film image, the interpolation unit 30 executes spatial interpolation using data of an interpolation target field only. However, if the film determination unit 20 determines that the input image is a film image, the interpolation unit 30 interpolates the interpolation target field using information of fields that are temporarily consecutive to the interpolation target field.
Accordingly, if the input image is a film image, the interpolation unit 30 of the conventional image processing device interpolated a current field using a previous field or a next field of the current field that is selected on the basis of the pattern generated by the pattern detection unit 10. However, judder may occur in an image processed by the conventional image processing device because the generated pattern might have an error, or a field that is not originated from the same progressive frame, such as a bad-edit, is used for interpolation. A bad-edit is detected when the sequence of a 3:2 pull-down image steam or a 2:2 pull-down image stream is inverted during the edition, losing the regularity of the pull-down.